1. Field of the Invention
This invention relates to an image recording apparatus for irradiating an optical pattern to a photosensitive material, such as photographic paper, and thereby recording an image, which is represented by the optical pattern, on the photosensitive material. This invention particularly relates to an image recording apparatus for recording a color image by use of a spatial light modulator.
2. Description of the Prior Art
There have heretofore been carried out operations for irradiating light to a photosensitive material, such as photographic paper or a heat development photosensitive material, developing the thus exposed photosensitive material, and thereby obtaining the optical pattern as a visible image. As the techniques for irradiating the optical pattern to the photosensitive material, various techniques have heretofore been carried out. For example, with techniques using ordinary enlarging apparatuses or printers, light having passed through a negative film is projected onto photographic paper. With different techniques, an image signal, which has been obtained by photoelectrically reading out an image recorded on a negative film, is fed into a cathode ray tube (CRT) display device, and light radiated out from the CRT display device is directly irradiated to a photosensitive material. With further different techniques, a laser beam is modulated with an image signal, and the thus modulated laser beam is scanned on a photosensitive material.
Ordinarily, the sensitivity of photosensitive materials is not very high. Therefore, in cases where the aforesaid techniques using the CRT display device is employed, it is necessary for the luminance of the CRT display device to be set at a high level. However, if the luminance of the CRT display device is set at a high level, the spot diameter of the CRT display device will become large, and therefore the resolution of the image recorded on the photosensitive material cannot be kept high. Also, in order for the image to be recorded on the photosensitive material such that the resolution may be kept high, it is necessary for the irradiation of the optical pattern from the CRT display device to be carried out for a long time.
With the techniques wherein a laser beam is irradiated to the photosensitive material, the laser beam is quickly scanned on the photosensitive material and therefore a certain point on the photosensitive material is exposed to light only for a very short time. As a result, the problems occur with regard to a reciprocity law failure occur, in which the exposure amount necessary for yielding a specific level of image density varies in accordance with the conditions of the illuminance of light and the irradiation time. Accordingly, it is necessary for a specific photosensitive material free from the reciprocity law failure to be used, and general-purpose photosensitive materials cannot be used.
In view of the above circumstances, the applicant proposed an image recording apparatus, with which an image of a high resolution can be recorded quickly on a general-purpose photosensitive material, and a method of using the image recording apparatus. The image recording apparatus and the method of using it are disclosed in Japanese Unexamined Patent Publication No. 7(1995)-270746.
One image recording apparatus disclosed in Japanese Unexamined Patent Publication No. 7(1995)-270746 substantially comprises:
i) a single spatial light modulator, which comprises a photoconductive layer and an electro-optic material layer located with a light reflecting layer intervening therebetween, the spatial light modulator operating such that an optical pattern may be optically inputted from the side of the photoconductive layer into the spatial light modulator, and the optical pattern may thereby be written into the spatial light modulator, and such that reading light may be irradiated from the side of the electro-optic material layer to the spatial light modulator and may be reflected from the light reflecting layer, and the optical pattern, which has been written into the spatial light modulator, may thereby be read from the spatial light modulator,
ii) an optical pattern input means, which inputs blue (B), green (G), and red (R) optical patterns into the spatial light modulator, and
iii) an optical pattern reading means comprising:
a) a light source for irradiating B reading light, G reading light, and R reading light to the spatial light modulator in synchronization with the inputting of the B, G, and R optical patterns, respectively, and PA1 b) an optical system for irradiating the optical patterns, which have been read from the spatial light modulator, to a color photosensitive material, PA1 a) a light source for irradiating B reading light, G reading light, and R reading light to the spatial light modulator in synchronization with the inputting of the B, G, and R optical patterns, respectively, and PA1 b) an optical system for irradiating the optical patterns, which have been read from the spatial light modulator, to a color photosensitive material,
the image recording apparatus recording a color image, which is represented by the optical patterns, on the color photosensitive material.
As the electro-optic material layer, which constitutes the spatial light modulator described above, a liquid crystal layer having an operation mode, such as an electrically controlled birefringence (ECB) mode, is used popularly.
A technique, wherein a dielectric multi-layer film mirror, which is made up of 15 layers constituted of ZnS and MgF.sub.2, is used as a light reflecting layer, which is located between a photoconductive layer and an electro-optic material layer in a spatial light modulator of the type described above, is disclosed in, for example, Applied Physics Letters, Vol. 22, No. 3, 1973, pp. 90-92.
Also, a spatial light modulator, wherein a specific light reflecting layer is employed, the resistance of the light reflecting layer along its intra-surface direction is thereby kept to be large, and the resolution is enhanced, is disclosed in, for example, Japanese Unexamined Patent Publication No. 3(1991)-107818. In the disclosed spatial light modulator, the light reflecting layer is constituted of an Si-Ge/SiO.sub.2 alternate multi-layer film, in lieu of an SiO.sub.2 /Si alternate multi-layer film mirror and a TiO.sub.2 /SiO.sub.2 alternate multi-layer film mirror.
Further, a spatial light modulator, wherein a light reflecting layer is constituted of an alternate multi-layer film mirror, which comprises SiO.sub.2 films and Si or Ge light absorbing films located alternately, is disclosed in, for example, Japanese Unexamined Patent Publication No. 3(1991)-217825. By the use of the alternate multi-layer film mirror as the light reflecting layer, the mirror layer is imparted with the functions for a light blocking layer. In this manner, voltage loss in the mirror layer and a light blocking layer is reduced, spread of the line of electric force is reduced, and the contrast ratio and the resolution are enhanced.
With the spatial light modulators described above, as described also in Japanese Unexamined Patent Publication No. 3(1991)-107818, if the electrical conductivities of the light reflecting layer and a light blocking layer, which is located together with the light reflecting layer, along their intra-surface directions are high, a good image cannot be obtained. Therefore, in cases where the light reflecting layer and the light blocking layer are made from a material having a high electrical conductivity, such as a metal, the light reflecting layer and/or the light blocking layer is subjected to patterning with respect to picture elements, and the picture elements are thereby insulated from one another. Alternatively, as disclosed also in Japanese Unexamined Patent Publication No. 3(1991)-107818, a countermeasure is taken in order to reduce the electrical conductivity as much as possible.
In view of the above circumstances, the light reflecting layer is often constituted of a dielectric multi-layer film mirror having the electrical insulating properties. Ordinarily, in cases where the light reflecting layer is constituted of an electrical insulating material, an electric field, which acts upon the electro-optic material layer in order to form an image, spreads in the transverse direction as it passes through the layers having the electrical insulating properties, such as the light reflecting layer, the light blocking layer, and the electro-optic material layer. Therefore, as the thicknesses of the layers having the electrical insulating properties become large, the resolution becomes low.
Also, in particular, in the spatial light modulator of the type in which an optical pattern is inputted optically, since voltage loss arises due to the layers having the electrical insulating properties described above, the problems described below occur. Specifically, as the electric capacities of the layers having the electrical insulating properties become small (i.e., as the layer thicknesses of the layers having the electrical insulating properties become large), the amount of modulation of the electric field, which is applied to the electro-optic material layer, becomes small, and the sensitivity becomes low.
Accordingly, it is required that the layer thickness of the light reflecting layer in the spatial light modulator be kept as thin as possible.
Further, in cases where the spatial light modulator is utilized in the aforesaid color image recording apparatuses, color video projectors, or the like, such that the light utilization efficiency may be kept high, the absolute reflectance of the light reflecting layer should preferably be as high as possible. Also, such that no tinting may occur with respect to the entire range of the visible wavelength region, the spectral reflectance of the light reflecting layer should preferably be as flat as possible.
As the dielectric multi-layer film mirror which constitutes the light reflecting layer, a mirror constituted of a multi-layer film comprising repeated quarter-wave layers with respect to a single center wavelength has heretofore been known widely. Ordinarily, such a dielectric multi-layer film mirror is not provided with an effect range capable of covering the entire range of the visible wavelength region. Therefore, a plurality of dielectric multi-layer film mirrors with respect to two or more center wavelengths must be combined together. However, in such cases, the total thickness of the combined mirrors cannot be kept small, and the resolution and the sensitivity cannot be kept high.